Metabolite to parent drug concentration ratio as a function of parent drug extraction ratio: Cases of nonportal route of administration

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Abstract
The ratio of metabolite to parent drug concentration (Cm/Cp)of a medium or high extraction ratio (E>0.1)drug administered intravenously has been shown to depend on intrinsic clearance of drug by other metabolic routes (CLr,int)as well as on organ blood flow (Q).In contrast, for a low extraction ratio drug given intravenously or for any drug given by a portal route, this ratio is equal to the ratio of formation clearance (CLf,int)and metabolite clearance (CLm,int).The sensitivity of Cm/Cpto changes in CLr,intand CLf,inthas been analyzed quantitatively. It was shown to be dependent on the fraction metabolized to that particular metabolite (fm).